The present invention relates to the construction of printers, especially large format printers, and more particularly to the printer chassis and to the arrangement of the other printer components therein.
When constructing a printer, conflicting design constraints arise. A robust structure is required so that the printer can withstand the considerable dynamic forces which arise in use. Furthermore, unwanted vibrations or movements can cause a deterioration of print quality. On the other hand, certain components require to be precisely located and possibly adjusted during use. The problems are particularly acute in large format printers, in which the support points for components such as beams can be a considerable distance apart.
In some prior art printers, cover members constitute structural members, but this restricts the aesthetic design of the printer, adds weight to the printer, and requires the covers to be attached when testing the printer. In U.S. Pat. No. 5,195,836, the printer chassis comprises as its main structural member a rigid support beam which is connected at its ends to two parallel structural sideplates. The sideplates provide cradles for the printer carriage slider rods. These rods are precisely positioned by a system of yoke members which are connected to the main support beam and are supported at openings in the sideplates. The sideplates are allowed to flex in the longitudinal direction of the rods, e.g. under the effects of temperature, so as not to affect the vertical position or straightness of the rods.
U.S. Pat. No. 5,600,360 discloses a frame for mounting a printer carriage with upper and lower beams having their ends directly connected to sideplate members. French Patent 2539354 discloses a printer with beams, each beam having its own sideplates.
The present invention seeks to provide a relatively simple printer chassis construction which is robust and permits precise location of components where required, and yet provides wide design flexibility, e.g. in terms of the positioning and attachment of the other components of the printer, such as the ink supply system, and in the nature and functioning of cover members of the printer.
According to a first aspect of the present invention there is provided a printer chassis comprising a first structural beam with means to support a printer carriage, and two structural sideplate members arranged to be attached to said first beam, wherein said first beam is directly attached to each said sideplate member such that said sideplate members are spaced from the ends of said first beam so that it extends at both ends beyond said sideplate members, and the chassis comprises one or more further structural beams of the same material as said first beam and extending between said sideplate members.
The term xe2x80x9cstructuralxe2x80x9d means that the members concerned support the weight and/or control the deformations of other parts of the system.
Preferably, said first beam is attached to each sideplate member by means of a plurality of attachment points which extend in a straight line. Such a connection acts as a type of hinge which protects the first beam from the adverse effects of deformations of the sideplate members, both during attachment of the further structural beams and during subsequent use of the printer.
Preferably each beam comprises a plurality of channels of at least part-circular cross-section which are arranged to align with corresponding apertures in the sideplate members to define self-tapping screw connections. This enables the beams to be produced by an extrusion method, without the need for special machining steps at the attachment points.
Preferably the printer carriage support means support slider rod means for the printer carriage which are secured to the support means at spaced intervals in the longitudinal direction by securing members which in a first region restrict relative movement in all directions and which, in at least one second region, permit limited relative movement in the longitudinal direction but restrict relative movement in the two mutually-orthogonal directions. This enables differential thermal movements to occur in the longitudinal direction, between the slider rod means (preferably steel) and the beam (preferably aluminium), without affecting the straightness of the slider rod means and their location relative to the sideplate members.
Preferably, the securing members have shaft portions which extend through apertures in the support means and openings in the slider rod means, and the apertures in a first region of the support means are of substantially the same size as the openings in the slider rod means whereas the apertures in at least one second region of the support means are of increased size in the longitudinal direction. The securing members are preferably threaded screws.
The securing members may be provided with resilient biasing means to control the securing force e between the slider rod means and said first beam. The securing force is substantially constant within a predetermined narrow range. The resilient biasing means are preferably helical springs around the shaft portions of the securing members. Without the springs it would not be feasible to obtain or maintain the constant force.
In preferred arrangements each sideplate member defines a respective seating for each of two slider rods, one of said seatings comprising a V-shaped groove, and the other of said seatings comprising a flat support surface. This enables the V-shaped groove to precisely reference the relative positions of the sideplate members to the slide rod which is in the groove (and thus to the printer carriage beam), whereas the flat surface supports the other slider rod in the vertical direction, but without over-specifying its location in the front/rear direction.
A printer apparatus may comprise a printer chassis as defined above together with at least one printer sub-unit having a plurality of projecting attachment elements, wherein the sidepalte members are provided with a plurality of apertures which are arranged to receive the projecting attachment elements. The projecting attachment elements preferably comprise stud and/or clip members and the arrangement is such that the sub-units can be readily and quickly attached to the printer chassis and subsequently detached therefrom.
According to a second aspect of the present invention, there is provided a method of assembling a chassis for a printer comprising a first structural beam, two structural sideplate members and one or more further structural beams of the same material as said first structural beam, wherein said first beam is firmly, precisely and directly fixed to each said sideplate member such that said sideplate members are spaced from the ends of said first beam and so as to define a reference for the relative location of the or each said further structural beam between said sideplate members.
Such a method provides a structure which is resistant to vibrations and deformations so as to permit a high printing quality.
According to a third aspect of the present invention there is provided printer apparatus comprising a printer carriage beam having elongate support means arranged to support at least one slider rod for mounting a printer carriage, wherein said rod and said beam are secured together at spaced intervals in the longitudinal direction by securing members wherein, in a first region, said securing members restrict relative movement in all directions and which, in at least one second region, said securing members permit limited relative movement in the longitudinal direction but restrict relative movement in the two mutually-orthogonal directions.
Such a printer apparatus has the previously-mentioned advantages.